Stores saturated with ads and promotions for cigarettes constitute a significant public health concern, especially for adolescents. Our previous research combined data from school-based surveys of middle school students at baseline, 12 months, and 30 months, with data from observations in all stores that sold cigarettes in the study community. Two measures of exposure to retail tobacco advertising were developed by: (a) assessing the frequency of visits to types of stores that contain the most tobacco advertising (convenience, small grocery, and liquor stores) and (b) eliciting information about where and how often adolescents shopped in tobacco outlets near school and assessing the quantity of cigarette marketing materials in those stores. Both exposure measures predicted significant increases in the odds of initiating smoking at each follow-up, and the more exposure adolescents reported, the greater their chances of experimenting. A second longitudinal study observed similar findings in an urban community with a higher concentration of tobacco outlets and a more racially diverse population. This proposal seeks continued funding to better understand the impact of the retail tobacco environment on smoking initiation at the national level. Adolescents (ages 13-16) will be surveyed at baseline, 8 months, and 16 months (n=1,350), using an existing Internet panel that is representative of U.S. households with telephones. An innovative feature of this research is the ability to link all respondents' data to their residential and school addresses, allowing simultaneous study of environmental and individual risk factors for smoking initiation. This research aims to: (a) determine whether our previous results about the impact of exposure to retail tobacco advertising on smoking initiation generalize from two California communities to a population-based survey of U.S. adolescents, and (b) test the hypothesis that the odds of smoking initiation are increased for adolescents in neighborhoods with higher tobacco outlet density, adjusting for both individual and neighborhood characteristics. Secondary analyses will compare different process explanations for the impact of retail tobacco advertising and tobacco outlet density on smoking initiation. This investigation will advance our understanding of the health risks associated with the availability of cigarettes and visibility of cigarette advertising in the environment and provide a scientific rationale for new policies to reduce them.